The present invention relates generally to a novel device for treating tissues within a patient and to novel methods for performing such treatments. More specifically, the invention relates to a novel energy treatment device, especially an electrophysiology, RF energy thermal tissue treatment device, and to methods of using such a device to treat tissues.
The human heart is an engineering marvel which can pump blood through a patient's body for, in some cases, over one hundred years without serious difficulty or complication. The heart itself is about the size of a clenched fist, and has four chambers which receive blood from, and pump blood through the body. Basically, blood courses through a patient's vascular system, supplying necessary elements to sustain life and removing wastes, such as carbon dioxide, from the body. Once the blood has passed through the vascular system, the blood returns to the heart, where it enters a first blood receiving chamber, referred to as the right atrium. The right atrium is connected to a first blood pumping chamber, called the right ventricle, by a valve which prevents back flow of blood from the right ventricle into the right atrium when the right ventricle contracts to pump blood. The right ventricle is also connected to a pulmonary artery for delivering blood to the lungs so that the blood can basically get rid of collected carbon dioxide and replace it with oxygen. This re-oxygenates the blood, and the blood is ready to course through the patient's body again.
After the blood has been re-oxygenated, the blood returns to the heart through a blood vessel called the pulmonary vein. The end of the pulmonary vein opposite to the end connected to the lungs is connected to a second blood receiving chamber of the heart, called the left atrium. The left atrium is connected to a second blood pumping chamber, known as the left ventricle, through a valve which prevents back flow of blood from the left ventricle into the left atrium as the left ventricle contracts. The left ventricle is also connected to a blood vessel, called the aorta, which accepts blood from the left ventricle and directs that blood into the patient's vasculature. In this way, re-oxygenated blood is returned to the body, where it can supply more necessities, like oxygen, and remove more wastes, like carbon dioxide.
The structure of the heart is particularly adept at performing repeated, regular contractions of the ventricles to preserve substantially constant blood flow through the patient's body. The tissues making up the heart generally comprise a layer of muscle and cardiac cells, called the myocardium, disposed between inner and outer lining layers of the heart. The muscle cells of the myocardium respond to electrical processes, pulses or stimuli to properly contract and relax in order to pump blood. Thus, there are two electrical processes which take place during pumping of blood by the heart. The first, called depolarization, occurs when muscle cells of the myocardium are stimulated, thereby causing the myocardium to contract, which forces blood out of the ventricles. The second process is called repolarization wherein the muscle cells of the myocardium relax, thereby allowing blood to flow into the ventricles from the appropriate atrium. For these processes to occur properly, thereby insuring proper blood flow, the stimulation of the muscle cells of the myocardium must be regular. If this stimulation is not regular, then the heart may not function properly, which may compromise the patient's health. The muscle cell stimuli are often carried within the myocardium along specific, correct pathways which can provide for regular stimulation of the muscle cells. However, if these correct pathways are not followed, the stimulation of the muscle cells may become irregular.
There are at least two ways by which the stimulation of the muscle cells of the myocardium may become irregular. The first will be called the accessory pathway condition for the purposes of this disclosure; the second being called the infarct-related condition. The accessory pathway condition can be generally characterized by a condition where the electrical stimuli travel through other, accessory stimuli pathways, in addition to the proper pathways. These other, accessory pathways which are formed on the heart result in irregular stimulation of the muscle cells. The accessory pathway condition often exists at birth, and may be caused by a malformation of the heart. This condition, although it exists at birth, may not show up in a relatively young heart. This condition may worsen over time and lead to irregular stimulation of the muscle cells and irregular pumping of blood.
One method of treating the accessory pathway condition is by electrophysiology ablation of portions of the heart. This treatment method takes advantage of the fact that the correct pathways of muscle cell stimulation, as well as the accessory pathways exist within the heart. If the accessory pathways are effectively eliminated, then muscle cell stimulation will take place only along the correct pathways discussed earlier, thereby leading to a substantially regular heart beat. In order to effectively eliminate the accessory pathways, an electro-ablation or mapping catheter is used to apply radio frequency (hereinafter "RF") electrical energy to the accessory pathways.
Specifically, a mapping catheter, well known to those having ordinary skill in the relevant art, is placed within the heart to map the heart and locate the accessory pathways in known fashion. Once the accessory pathways are located, the distal end of the mapping catheter is placed adjacent a location of an accessory pathway in the heart. The mapping catheter may have a suitable conductor, such as an electrode, or other suitable RF energy transmission device, located on the distal end of the catheter for supplying RF energy to the heart. RF energy is supplied to the relevant portions of the heart to disrupt stimuli transmission along the accessory pathway. Specifically, sufficient RF energy is applied to the heart to heat, and thereby ablate, that portion of the heart. Ablation of the portion of the heart changes that portion into scar tissue. Since scar tissue does not conduct muscle cell stimuli as readily as healthy portions of the heart, the accessory pathways are effectively eliminated.
In order to perform effective elimination of the accessory pathways by delivery of RF energy, the distal tip of the mapping catheter, and specifically the electrode, must be physically engaged against the portion of the heart associated with the accessory pathway. This is necessary to insure proper energy transmission to the pathway to be eliminated. This physical engagement must be maintained throughout the treatment. Maintaining the physical engagement may be difficult, especially upon consideration that the heart is continuously moving as it beats. In addition, the RF energy present in the distal tip conductor can dehydrate or otherwise affect blood adjacent the conductor. Thus, blood can coagulate around the conductor forming blood clots or coagulum. Because clotted blood does not conduct electrical energy well, the blood clots on the conductor can electrically insulate the conductor, thereby further limiting the efficiency of RF energy transmission to the relevant portions of the heart. If sufficient blood clot material forms on the conductor, the entire mapping catheter may have to be removed from the patient and cleaned. Once cleaned, the mapping catheter will have to be reinserted into the patient's heart to complete the treatment. This procedure of catheter removal, cleaning, and reinsertion may take considerable time, on the order of one half of one hour or so, which may not be beneficial to the patient. In addition, thermal energy may be generated in the distal tip conductor, thereby further reducing the efficiency of RF energy transmission to the heart tissue. Specifically, the thermal energy may dry out or desiccate adjacent blood and tissues, thereby creating a high impedance at the conductive interface between the tissues to be treated and the conductor. The high impedance may reduce the flow of current to the tissues and the amount of energy that can be delivered thereto. Thus, the depth of energy penetration into the tissues may be correspondingly limited.
Similar occurrences can be encountered with the infarct-related condition causing irregular transmission of muscle cell stimuli. Myocardial infarction is the technical term for the destruction or death of cells which make up the myocardium by events such as a heart attack. The infarct-related condition is characterized by certain cells in the myocardium being damaged such that they do not conduct muscle cell stimuli properly. Specifically, the damaged cells may not contract in response to stimuli in a regular fashion, thereby forming what is referred to as a re-entrant circuit in the heart. This too can cause irregular heart function.
The infarct-related condition is treated in substantially the same manner as described above. A mapping catheter is inserted into the patient's heart to locate the sites of re-entrant circuits. Once these sites are found, the conductor on the distal tip of the mapping catheter is physically engaged against the identified portions of the heart to supply RF energy to the site. The site is heated by the RF energy sufficiently to effectively eliminate the re-entrant circuit, thereby restoring substantially normal heart function. This treatment method, however, is also subject to the same concerns discussed earlier with respect to maintaining the physical engagement of the electrode and the heart, blood clotting, and tissue desiccation effects.
The above-discussed RF ablation treatment techniques and devices can comprise an effective treatment means for certain defects in heart functionality. However, these techniques and devices do have the disadvantages described above which may make their performance suboptimal in certain situations. Accordingly, it is desirable to provide an improved method and device for performing RF ablation treatment of tissues within a patient's body which are not subject to the concerns discussed in detail in the preceding paragraphs. The present invention is intended to provide such an improvement.
Specifically, the present invention provides improved, novel devices and methods for performing energy treatment, and specifically electrophysiology RF energy treatment of tissues within a patient's body. Preferably, the novel devices and methods will not be as subject to the concerns regarding physical engagement maintenance and blood coagulating or clotting on a conductor as are some similar devices and methods of the prior art. The novel devices and methods may be applicable in subjecting to RF energy, and the like, tissues located in various portions, such as a coronary portion or a peripheral portion, of a patient's body.